1. Field of the Invention
The present invention relates to a magnetic bearing device with a vibration restraining function, a magnetic bearing device with a vibration estimating function, and a pump device with the magnetic bearing devices mounted thereto. More specifically, the invention relates to a magnetic bearing device with a vibration restraining function, a magnetic bearing device with a vibration estimating function, and a pump device with the magnetic bearing devices mounted thereto, in which it is possible to realize a reduction in vibration in the apparatus system as a whole inclusive of the equipment associated with the vacuum pump without newly providing a vibration sensor.
2. Description of the Related Art
With the recent years' development of electronics, there is a rapidly increasing demand for semiconductors for forming memories, integrated circuits, etc.
Such semiconductors are manufactured, for example, by doping a semiconductor substrate of a very high purity with impurities to impart electrical properties thereto, or by stacking together semiconductor substrates with minute circuit patterns formed thereon.
The operation of manufacturing such semiconductors must be conducted in a high vacuum chamber in order to avoid the influences of dust, etc. in the air. This chamber is generally evacuated by a vacuum pump. In particular, a turbo-molecular pump, which is a kind of vacuum pump, is widely used since it entails little residual gas and is easy of maintenance.
A semiconductor manufacturing process includes a number of steps in which various process gases are caused to act on a semiconductor substrate, and the turbo-molecular pump is used not only to evacuate the chamber but also to discharge these process gases from the chamber.
Further, in an apparatus like an electron microscope, an turbo-molecular pump is used to create a high vacuum state in the chamber of the apparatus in order to prevent refraction, etc. of an electron beam due to the presence of dust or the like.
Such a turbo-molecular pump is composed of a turbo-molecular pump main body for sucking and discharging gas form the chamber of a semiconductor manufacturing apparatus, and electron microscope, or the like, and a control device for controlling the turbo-molecular pump main body.
FIG. 10 is a longitudinal sectional view of a turbo-molecular pump main body, and FIG. 11 is a schematic diagram showing an apparatus system as a whole in which the turbo-molecular pump main body is used to evacuate a chamber.
In FIG. 10, a turbo-molecular pump main body 100 includes an outer cylinder 127, on top of which there is formed an intake hole 101. Provided inside the outer cylinder 127 is a rotor 103 having in its periphery a plurality of rotary blades 102a, 102b, 102c, . . . serving as turbine blades for sucking and discharging gas and formed radially in a number of stages.
At the center of the rotor 103, there is mounted a rotor shaft 113, which is supported in a levitating state and controlled in position, for example, by a so-called 5-axis control magnetic bearing.
Upper radial electromagnets 104 consist of four electromagnets arranged in pairs in X- and Y-axis directions, perpendicular to each other, and opposed to each other with the rotor shaft 113 therebetween. It is to be assumed that the X- and Y-axes are in plane perpendicular to the axis of the rotor shaft 113 when the rotor shaft 113 is at a control target position of the magnetic bearing. Further, there is provided an upper radial sensor 107 consisting of four coils wound around cores and arranged in close proximity to and in correspondence with the upper radial electromagnets 104. The upper radial sensor 107 detects radial displacement of the rotor 103, transmitting a detection signal to a control device 200 shown in FIG. 11.
The control device 200 is equipped with magnetic bearing feedback control means composed of a compensator 201, an amplifier 202, etc. In this control device 200, excitation of the upper radial electromagnets 104 is controlled by the output of the amplifier 202 supplied through the compensator 201 having a PID adjusting function, on the basis of a displacement signal detected by the upper radial sensor 107, thus performing adjustment of the radial position of the upper portion of the rotor shaft 113.
The rotor shaft 113 is formed of a high-magnetic-permeability material (e.g., iron) and is adapted to be attracted by the magnetic force of the upper radial electromagnets 104. Such adjustment is conducted independently in the X-axis direction and the Y-axis direction.
Further, lower radial electromagnets 105 and a lower radial sensor 108 are arranged in the same way as the upper radial electromagnets 104 and the upper radial sensor 107. Like the radial position of the upper portion of the rotor shaft 113, the radial position of the lower portion of the rotor shaft 113 is adjusted by the magnetic bearing feedback control means in the control device 200.
Further, axial electromagnets 106A and 106B are arranged respectively on the upper and lower sides of a metal disc 111 provided in the lower portion of the rotor shaft 113. The metal disc 111 is formed of a high-magnetic-permeability material, such as iron. To detect axial displacement of the rotor 103, there is provided an axial sensor 109, which transmits an axial displacement signal to the control device 200.
The axial electromagnets 106A and 106B are excitation-controlled by the output of the amplifier 202 supplied through the compensator 201, which has a PID adjusting function, of the control device 200, on the basis of the axial displacement signal. The axial electromagnet 106A magnetically attracts the metal disc 111 upwardly, and the axial electromagnet 106B magnetically attracts the metal disc 111 downwardly.
In this way, in the control device 200, the magnetic force the axial electromagnets 106A and 106B exert on the metal disc 111 is appropriately controlled by the magnetic bearing feedback control means, magnetically levitating the rotor shaft 113 in the axial direction and retaining it in the space in a non-contact state.
A motor 121 is equipped with a plurality of magnetic poles consisting of permanent magnets arranged circumferentially on the rotor side so as to surround the rotor shaft 113. A torque component for rotating the rotor shaft 113 is imparted to these permanent magnet magnetic poles from the electromagnets on the stator side of the motor 121, thereby rotating the rotor 103.
Further, an RPM sensor and a motor temperature sensor (not shown) are mounted to the motor 121, and the rotation of the rotor shaft 113 is controlled in the control device 200 in response to detection signals from the RPM sensor and the motor temperature sensor.
A plurality of stationary blades 123a, 123b, 123c, . . . are arranged so as to be spaced apart from the rotary blades 102a, 102b, 102c, . . . by small gaps. In order to downwardly transfer the molecules of exhaust gas through collision, the rotary blades 102a, 102b, 102c, . . . are inclined by a predetermined angle with respect to a plane perpendicular to the axis of the rotor shaft 113.
Similarly, the stationary blades 123 are also inclined by a predetermined angle with respect to a plane perpendicular to the axis of the rotor shaft 113, and extend toward the inner side of the outer cylinder 127 to be arranged alternately with the rotary blades 102.
The stationary blades 123 are supported at one end by being inserted into gaps between a plurality of stationary blade spacers 125a, 125b, 125c, . . . stacked together in stages.
The stationary blade spacers 125 are ring-shaped members, which are formed of a metal, such as aluminum, iron, stainless steel, or copper, or an alloy containing such metal as a component.
In the outer periphery of the stationary blade spacers 125, the outer cylinder 127 is secured in position with a small gap therebetween. At the bottom of the outer cylinder 127, there is arranged a base portion 129, and a threaded spacer 131 is arranged between the lowermost one of the stationary blade spacers 125 and the base portion 129.
In the portion of the base portion 129 below the threaded spacer 131, there is formed a discharge outlet 133. Connected to the discharge outlet 133 is a dry-sealed vacuum pump passage (not shown), and the discharge outlet 133 is connected to a dry-sealed vacuum pump (not shown) through this dry-sealed vacuum pump passage.
The threaded spacer 131 is a cylindrical member formed of a metal, such as aluminum, copper, stainless steel, or iron, or an alloy containing such metal as a component, and has a plurality of spiral thread grooves 131a in its inner peripheral surface.
The spiral direction of the thread grooves 131a is determined such that when the molecules of the exhaust gas move in the rotating direction of the rotor 103, these molecules are transferred toward the discharge outlet 133.
Connected to the lowermost one of the rotary blades 102a, 102b, 102c, . . . of the rotor 103 is a cylindrical portion 102d, which extends vertically downwards. The outer peripheral surface of this cylindrical portion 102d sticks out toward the inner peripheral surface of the threaded spacer 131, and is in close proximity to the inner peripheral surface of the threaded spacer 131 with a predetermined gap therebetween.
The base portion 129 is a disc-like member constituting the base of the turbo-molecular pump main body 100, and is generally formed of a metal, such as iron, aluminum, or stainless steel. The base portion 129 physically retains the turbo-molecular pump main body 100, and also functions as a heat conduction passage. Thus, the base portion 129 is preferably formed of a metal that is rigid and of high heat conductivity, such as iron, aluminum, or copper.
Further, connected to the base portion 129 is a connector 160, to which is connected a signal line between the turbo-molecular pump main body 100 and the control device 200.
In the above-described construction, when the rotary blades 102 are driven and rotated by the motor 121 together with the rotor shaft 113, an exhaust gas from a chamber 300 shown in FIG. 11 is sucked in through the intake hole 101, due to the action of the rotary blades 102 and the stationary blades 123.
The exhaust gas sucked in through the intake hole 101 passes between the rotary blades 102 and the stationary blades 123, and is transferred to the base portion 129. The exhaust gas transferred to the base portion 129 is sent to the discharge outlet 133 while being guided by the thread grooves 131a of the threaded spacer 131.
Further, in order to prevent the exhaust gas sucked in through the intake hole 101 from entering the electrical portion composed of the motor 121, the upper radial electromagnets 104, the upper radial sensor 107, the lower radial electromagnets 105, the lower radial sensor 108, etc., the electrical portion is covered with a stator column 122, and the interior of this electrical portion is maintained at a predetermined pressure with a purge gas.
For this purpose, the base portion 129 is equipped with piping (not shown), and the purge gas is introduced through the piping. The purge gas introduced is passed through the gap between a protective bearing 120 and the rotor shaft 113, the gap between the rotor and stator of the motor 121, and the gap between the stator column 122 and the rotary blades 102 before it is transmitted to the discharge outlet 133.
The turbo-molecular pump main body 100 requires identification of the model and control based on individually adjusted specific parameters (e.g., characteristics corresponding to the model). To store the control parameters, the turbo-molecular pump main body 100 contains an electronic circuit portion 141. The electronic circuit portion 141 is composed of a semiconductor memory, such as EEP-ROM, electronic parts, such as semiconductor devices for access to the semiconductor memory, a substrate 143 for mounting these components thereto, etc.
This electronic circuit portion 141 is accommodated under an RPM sensor (not shown) near the center of the base portion 129 constituting the lower portion of the turbo-molecular pump main body 100, and is closed by a hermetic bottom cover 145.
Incidentally, a reduction in vibration is required of the turbo-molecular pump main body 100, which is used for the chamber 300 of a semiconductor manufacturing apparatus, an electron microscope, or the like.
For example, when vibration is generated in the chamber 300 of the semiconductor manufacturing apparatus during exposure of a circuit pattern, misregistration with a lower circuit pattern will occur, making it impossible to perform normal circuit operation.
Further, in the case of the chamber 300 of the electron microscope also, upon generation of vibration while an object is being observed, the object will be out of focus, resulting in image disturbance.
In view of this, as shown in FIG. 11, the turbo-molecular pump main body 100 is suspended from the chamber 300 through the intermediation of a pump damper 301.
The pump damper 301 shown in FIG. 11 is equipped with a bellows 302, around the outer periphery of which a rubber member 306 is wrapped. Between the turbo-molecular pump main body 100 and the chamber 300, the vibration due to the rotation of the rotor 103 is absorbed. One end of the bellows 302 is fastened to the chamber 300 through the intermediation of a flange (not shown), and the other end thereof is fastened to the intake hole 101 of the turbo-molecular pump main body 100 through the intermediation of a flange 303.
Further, the chamber 300 is supported by a frame 402 arranged on a floor 400, and a device damper 401 is provided between the chamber 300 and the frame 402.
Like the pump damper 301, this device damper 401 also absorbs vibration between the frame 402 and the chamber 300.
In the above-described construction, even if vibration is generated in the turbo-molecular pump main body 100, the vibration is absorbed by the pump damper 301, so that it is not easily transmitted to the chamber 300.
Further, vibration generated from the floor 400 is similarly absorbed by the device damper 401, and is not easily transmitted to the chamber 300.
In this way, a reduction in vibration is achieved for the chamber 300.
However, in the case of vibration damping with such a mechanical damper, there is a problem in that it is rather difficult to achieve a satisfactory vibration damping effect, in particular, in the low-frequency band, for a vibration transmitted through the turbo-molecular pump main body 100 and the frame 402.
Thus, a plurality of pump dampers 301 and a plurality of device dampers 401 are provided in series between the chamber 300 and the turbo-molecular pump main body 100 and between the chamber 300 and the frame 402, respectively, thereby achieving an improvement in terms of vibration damping effect for the chamber 300. However, to cope with the recent years' miniaturization in semiconductor manufacturing process, increase in resolution for electron microscopes, etc., there is a demand for a further reduction in vibration in low-frequency bands.
Further, as a result of the recent increase in the volume of the chamber 300 of a semiconductor manufacturing apparatus or the like, there is a demand for an increase in evacuation speed for the turbo-molecular pump main body 100. To cope with this, the turbo-molecular pump main body 100 and the pump damper 301 have been increased in size.
If its vibration damping effect is to be maintained at a fixed level or more, such an increase in the size of the pump damper 301 could lead to an increase in cost.
Further, the dry-sealed vacuum pump (not shown) connected to the turbo-molecular pump main body 100 generates vibration, which, although small, is transmitted to the turbo-molecular pump main body 100, etc. through the dry-sealed vacuum pump passage, causing the chamber 300 to vibrate. Further, vibration generated by this dry-sealed vacuum pump and other semiconductor manufacturing apparatus, etc., vibration generated by people walking, etc. are also transmitted to the floor 400, and may cause the chamber 300 to vibrate.
Such vibration of the chamber 300 cannot be avoided by reducing the vibration of the turbo-molecular pump main body 100 itself, and there is a demand for a reduction in vibration in the apparatus system as a whole including not only the turbo-molecular pump main body 100 but also the chamber 300.
To solve this problem, JP 2002-147454 A discloses a rotary machine equipped with a magnetic bearing device capable of reducing vibration in a place spaced apart from the magnetic bearing to some degree. In the rotary machine equipped with this magnetic bearing device, a vibration detecting sensor is arranged on the flange 303 of the pump damper 301, a flange (not shown) on the chamber 300 side or the like, and, on the basis of a detection signal detected by this vibration detecting sensor, reverse-phase vibration is imparted to the rotor 103, thereby canceling the vibration of the apparatus system as a whole.
However, in the case of JP 2002-147454 A, it is necessary to newly prepare a vibration detecting sensor for the turbo-molecular pump main body 100, resulting in an increase in parts cost Further, since this vibration detecting sensor is arranged on the pump damper 301 side, the chamber 300 side, etc., it is necessary to secure previously an installation space around the pump damper 301, the chamber 300, etc., and, to establish communication between the vibration detecting sensor and the control device 200, it is necessary to newly provide a signal line between the pump damper 301, the chamber 300, etc.